1. Field of the Invention
The present invention relates to an electronic image pickup apparatus, more particularly, to an electronic image pickup apparatus including a zoom lens system having a reflective element.
2. Description of the Related Art
In recent years, instead of a 35 mm silver halide film camera (135 formats), a digital camera (an electronic camera) has been a mainstream which photographs a subject by use of an electronic image pickup device such as a CCD image sensor or a CMOS type image sensor. Furthermore, the camera has a large number of categories in a broad range from a highly functional type for business to a portable popular type.
Especially, in the category of the portable popular type, it has been demanded that a conveniently usable electronic image pickup apparatus (a video camera, a digital camera or the like) including a zoom lens system and having a small size in a depth direction be provided.
The largest problem (bottleneck) which hampers thinning of the camera in the depth direction is a thickness of an optical system, especially the zoom lens system from a surface closest to an object side to an image pickup surface. In recent years, as a mainstream of a camera body thinning technology, a so-called collapsible lens barrel is employed in which the optical system projects from a camera body during photographing, but the system is stored when carried.
However, in a case where the collapsible lens barrel is employed, much time is required for starting the apparatus so as to bring stored lenses into a usable state, which is unfavorable for usability. When a lens unit closest to the object side is movable, many disadvantages are generated from a viewpoint of waterproof or dust-proof design.
In one of constitutions which have been developed in recent years, an optical path (an optical axis) of the optical system is bent by a reflective optical element such as a mirror or a prism so as to provide a camera remarkably thin in the depth direction. The constitution is favorable since, unlike the collapsible lens barrel, a startup time to bring the camera into the usable state (a time to extend the lenses) is not required and water-proof or dust-proof design may be easily introduced.
In the constitution, the lens unit closest to the object side is fixed in a direction along the optical axis, the lens unit is provided with the reflective optical element, the optical path reflected by the optical element extends in a vertical or horizontal direction of the camera body, and a dimension of the electronic image pickup apparatus in the depth direction is set to be as small as possible.
A zoom lens system in which the optical system capable of achieving the thinning of the apparatus and which is of a positive-lead lens type (the lens unit closest to the object side has a positive refractive power) is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2004-354,871 and 2004-354,869.
However, such a lens type is constituted so that a composite system of a first lens unit and a second lens unit has a negative refractive power in a wide-angle end, but the total length of the whole system easily increases. The zoom lens system of the positive-lead lens type is largely influenced by a manufacturing error.
On the other hand, in a zoom lens system of a negative-lead lens type (the lens unit closest to the object side has a negative refractive power), one lens unit closest to the object side in the wide-angle end has a negative refractive power, and the total length of the system is advantageously reduced. It is also known that the system is scarcely influenced by the manufacturing error.
As such a zoom lens system of the negative-lead lens type, a zoom lens system is disclosed in Japanese Patent Application Laid-Open No. 2005-338,344. This zoom lens system has, in order from the object side, a fixed negative lens unit, a positive lens unit which is movable for zooming, a fixed negative lens unit, and a fourth lens unit which moves along a track which is convex toward an image surface in order to compensate an image position.